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Appendix 4: Profiles of Colorado State-Listed Noxious Weeds 255 <br />Yellow toadflax (Linaria vulgaris) <br />Distribution: Yellow toadflax now occurs throughout the continental United States and in every Canadian province <br />and temtory (Saner et al, 7995). In Colorado, yellow toadflax is abundant on the Western Slope, but can be found <br />on the Front Range as well. It is typically found from 6,000 to 8,500 feet, but can be found up to 10,000 fee[. <br />Historical: Yellow toadflax was introduced from Eurasia as an ornamental. <br />Bioloev/Ecoloev <br />Life cycle: Spring emergence occurs azound mid-April and depends primarily on temperature. A smaller flush of <br />seedlings can occur in the fall. Prostrate stems emerge in September and produce leaves that are ovate, 0.9-1.5 <br />inches in size. Prostrate stems are tolerant to freezing and aze associated with floral stem production the following <br />yeaz (Robocker 1974). The strong, upright floral stems that are characteristic of mature toadflax plants develop after <br />a winter's dormancy, and emerge about the same time as seedlings in mid-April. Flowering occurs from May <br />through August and seeds mature from July through October (Saner et al. 1995). Yellow toadflax is self- <br />incompatible and relies on insects for pollination. The two most important pollinators aze bumblebees and halictid <br />bees (Zimmerman 1996). <br />Mode of reproduction: Yellow toadflax can reproduce both by seeds and vegetatively. Vegetative reproduction <br />enables a stand of toadflax to spread rapidly. Stems develop from adventitious buds on primary and lateral roots. <br />These buds can grow their own root and shoot system, and become independent plants the next yeaz. Yellow <br />toadflax colonies persist mostly via vegetation means while those of Dalmatian toadflax persist both by vegetative <br />and seed reproduction (Lajeunesse 1999). <br />Seed production: A mature plant can produce up to 30,000 seeds annually. A single stem has been reported to <br />contain over 5,000 seeds (Saner et al. 1995). <br />Seed bank: Seeds can remain dormant for up to ten years. <br />Dispersal: Winged seeds aid wind dispersal. Seeds may also be dispersed by water and ants (Rutledge, 1998). <br />Hybridization: No information available. <br />